CASCADE REFRIGERATION SYSTEM EMPLOYING NH_3 AND CO_2 – OPERATING EXPERIENCES FROM A FOOD PROCESSING PLANT

摘要

This paper describes the operating experiences associated with a medium size CO_2/NH_3 cascade refrigerationrnsystem installed in a commercial food processing facility in South East Queensland, Australia. Thernoperating experiences referred to are within the time period from commencement of commercial operation inrnNovember 2006 to early 2008. The large number of CO_2 compressor discharge pipe failures and how thesernproblems were remedied are described. The freezer store serviced by the CO_2 loop is provided with arnpenthouse type evaporator with two finned air cooling coils. The dry expansion feed to these coils, thernelectronic expansion valve control algorithm and the coil performance prediction are described. The CO_2rncompressor suction superheat recommended by the manufacturer is compared with the experiences fromrnpractical plant operation and possible CO_2 system simplifications are described. An alternative CO_2 receiverrnlocation and how this would impact on potential CO_2 losses during power outages is detailed.